You may be suffering from some database corruption. They way it comes and goes is unusual. You may want to run a database check through sypex (if you have it installed) or cpanel sql utils.
Connect to your site with a FTP client
Upload the file, overwriting the existing file in yoursite.com/yourforumsdirectory/library/EWRporta/Listener/Init.php
If you don't know how to do that, then send me a Private Message with your FTP credentials and I will do it for you.
Just that your error is clearly stating that it cannot find tar.php needed to unextract the "tar" archive game file.
Double check your archive_tar installation. Archive_Tar
Are you sure it's a nginx problem? Do you have Xenporta installed? I'll gladly take a look...but lets start with a simple URL and rule out the obvious issues first.
Some styles do some crazy things with the standard color variables. This is what causes this. Try tweaking the color properties of the style to get the affect you want.
How?
Use Chrome (inspect element) or Firefox's (firebug) to find the color variable you want to change and then change it...
You need to overwrite your Xenporta Init.php file with the one I posted here:
http://xfarcade.com/threads/xenforo-forges-forward-xfarcade.742/#post-2806